Device for detecting the attitude of motor vehicles

ABSTRACT

Described herein is a device for detecting the attitude of motor vehicles, which comprises using at least one filter of a complementary type for computing an estimate ({circumflex over (x)}i) of angles of attitude (θ, φ, ψ) of the motor vehicle as a function of input signals comprising an acceleration signal (A) and an angular-velocity signal (ω). According to the invention, the device (10) comprises a plurality of complementary filters (121, . . . , 12n) each tuned for operating in a specific dynamic range, and a supervisor unit (11), that acts to recognize the dynamic range of the input signals (A, ω) and select a corresponding filter (12i) from said plurality of complementary filters (121, . . . , 12n).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and all the benefits ofItalian Patent Application No. 10 2013 201 247.0, filed on Jan. 25,2013, both of which are hereby expressly incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a device for detecting the attitude ofmotor vehicles, using at least one filter of a complementary type toestimate angles of attitude of the motor vehicle.

2. Description of the Related Art

There are known in the sector of vehicles, including motor vehicles,inertial navigation systems (INSs) that enable, with respect to knownnavigation systems, based, for example, on GNSS signals, alternative orcomplementary navigation means. The INS records relative movements ofthe vehicle on which it is mounted and, on the basis of these, makesevaluations of the speed of the vehicle and the path followed.

The above INSs comprise inertial measurement units (IMUS) essentiallybased upon the measurements made by acceleration sensors and gyroscopes.In particular, these INSs use the measurements of accelerometers andgyroscopes to estimate angles of roll, pitch, and yaw of the motorvehicle, which enable evaluation of the attitude thereof.

INSs are based for the most part on extended Kalman filters (EKFs) inorder to estimate the above angles of attitude of the vehicle usingsensor-fusion techniques. This type of technique involves a high degreeof computational complexity, especially if there is available a largenumber of sensor channels, as well as difficulty of calibration asregards the observability matrix Q and the covariance matrix R of theKalman filter, and hence a high cost in terms of man hours for itsdevelopment.

An alternative solution envisages use of complementary filters, whichare instead easy to tune.

Various embodiments of complementary filters that can be used forproviding an estimator of attitude are illustrated, for example, in thepaper by Walter Higgins, “A comparison of complementary and Kalmanfiltering”, Aerospace and Electronic Systems, IEEE Transactions on(Volume: AES-11, Issue: 3), May 1975. However, complementary filters arevalid only for a specific dynamic range, in which the model of thevehicle can be linearly approximated.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved devicethat will enable use of filters with a lower degree of complexity,maintaining the performance of extended Kalman filters.

According to the present invention, the above object is achieved thanksto a device for detecting the attitude of motor vehicles that includesusing at least one filter of a complementary type for computing anestimate ({circumflex over (x)}_(i)) of angles of attitude (θ, φ, ψ) ofthe motor vehicle as a function of input signals comprising anacceleration signal (A) and an angular-velocity signal (ω). The deviceincludes a plurality of complementary filters, each tuned for operatingin a specific dynamic range, and a supervisor module, adapted torecognise the dynamic range of the input signals (A, ω) and select (S) acorresponding filter in said plurality of complementary filters.

Other objects, features and advantages of the present invention will bereadily appreciated as the same becomes better understood after readingthe subsequent description taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the annexeddrawings, which are provided purely by way of non-limiting example andin which:

FIG. 1 is a schematic perspective view of a device described herein;

FIG. 2 is a detailed view of a filter of the device of FIG. 1; and

FIG. 3 is a schematic view of an embodiment of a selector of the deviceof FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In brief, the solution according to the invention regards a device fordetecting the attitude of motor vehicles that comprises using at leastone filter of a complementary type to estimate angles of attitude of themotor vehicle, the device including a plurality of complementaryfilters, each tuned for operating in a specific dynamic range, and asupervisor unit, that acts to recognise the dynamic range of the inputsignals and select a corresponding filter in said plurality ofcomplementary filters.

Illustrated in FIG. 1 is a block diagram of an attitude-detection deviceaccording to the invention designated as a whole by the reference number10.

Shown at input to the above attitude-detection device 10 is a signalrepresenting an acceleration A of the motor vehicle, measured by anaccelerometer, not illustrated in FIG. 1. The aforesaid acceleration Aof the vehicle comprises components of acceleration with amplitudes ofacceleration A_(x), A_(y), A_(z) along three mutually perpendicular axesx, y, z, measured, for example, by a triaxial accelerometer device.

Moreover shown at input to the attitude-detection device 10 is a signalrepresenting an angular velocity ω of the vehicle measured by agyroscope, which is not illustrated in FIG. 1 either. This angularvelocity ω also comprises three components, p, q, r, expressed in theco-ordinates of the body, i.e., of the sensor.

The attitude-detection device 10 includes a bank 12 of complementaryfilters. This bank 12 of filters comprises a plurality of complementaryfilters 12 ₁, . . . , 12 _(n), each of which receives in parallel theacceleration signal A and the angular-velocity signal ω. Each i-thcomplementary filter 12 _(i) supplies at output a respective i-thestimate {circumflex over (x)}_(i) of the angles of attitude of thevehicle, i.e., angles of roll θ, pitch φ, and yaw ψ, as represented ingreater detail with reference to FIG. 2.

The attitude-detection device 10 further comprises a supervisor module11, which also receives at input the acceleration signal A and theangular-velocity signal ω, the velocities of the four wheels w_(s), andthe steering angle α and, on the basis of the values of these signals,controls, via a selection signal S, a selector 13 so that it connectsone of the outputs {circumflex over (x)}_(i) of the filters 12 _(i) toan output U of the attitude-detection device 10.

The above operation of tuning of each filter 12 _(i) for a differentdynamic range is obtained in particular by setting a value of arespective time constant τ of the filter 12 _(i), as described moreclearly in what follows with reference to FIG. 2. The filters 12 _(i)are equipped with different time constants τ, these different timeconstants τ rendering each filter 12 _(i) more suited to operating in adifferent dynamic range, i.e., to supplying an estimate {circumflex over(x)}_(i) of the angles of attitude of the vehicle that is more accuratein that particular dynamic range of the input signals.

The supervisor module 11 acts to detect the dynamic range associated tothe acceleration signal A and to the angular-velocity signal ω at inputgenerated by the vehicle while it is travelling and for selecting thecomplementary filter 12 _(i) tuned for the corresponding dynamic range.

In various embodiments, the supervisor module 11 acts to detect thelevel, i.e., the amplitudes A_(x), A_(y), A_(z) of the accelerationsignal A and the level, i.e., the amplitudes p, q, r of the angularvelocity that can be derived from the angular-velocity signal ω suppliedby the gyroscope.

In a preferred embodiment, the supervisor module may comprise, forexample stored in a memory of the microcontroller that implements it, aplurality of different models of the vehicle that estimate one or moreof the acceleration values A_(x), A_(y), A_(z) and/or of the signals ofthe gyroscope p, q, r, on the basis of other measured values of dynamicquantities of the vehicle that affect the value of the attitude in orderto identify the appropriate complementary filter to be used in theestimate of attitude.

The models stored are different in so far as they take into accountdifferent operating conditions of the vehicle, both in terms of dynamicrange (for example, range of speeds, acceleration, values of friction)and in terms of type of manoeuvre.

In this connection, FIG. 3 illustrates an example of supervisor 11comprising a plurality of different vehicle models 11 ₁, . . . , 11_(n).

The supervisor block 11 further comprises an evaluator block 111, thatevaluates which of the aforesaid vehicle models 11 ₁, . . . , 11 _(n)makes the best estimate of a current dynamic state of the vehicle. Onthe basis of the evaluation of the evaluator block 111, i.e., on thebasis of the j-th model 11 _(j) that best estimates the dynamic state ofthe vehicle, the model of the complementary filter 12 ₁, . . . , 12 _(n)to be used is chosen, by issuing a corresponding selection signal S.

In particular, in the example of FIG. 3, each model 11 _(j) supplies itsown estimates of the amplitudes of the accelerations Â_(yj), Â_(xj) onthe basis of the input data of the velocities of the four wheels w_(s)and on the basis of the steering angle α. Each vehicle model 11 _(j)estimates in an optimal way the accelerations Â_(yj), Â_(xj) in a givendynamic range of input quantities, i.e., values of the velocities of thefour wheels w_(s) and steering angle α, corresponding to given ranges ofthe dynamic quantities to be estimated, in the specific case theaccelerations Â_(yj), Â_(xj), which in turn correspond to a given valueof the time constant τ of the filter 12.

Evaluation of the vehicle model 11 _(j) in the evaluation block 111 may,for example, be carried out by measuring an error e_(j) as distance ofestimates Â_(x), Â_(y), Â_(z) of the accelerations from the accelerationvalues Ax, Ay, Az, effectively measured by the inertial platform. Ingeneral, this distance may be obtained via calculation of a norm appliedto these estimates Â_(x), Â_(y), Â_(z) and to the correspondingmeasurements A_(x), A_(y), A_(z).

The above norm may be of different types; for example, it may be a normthat calculates a Euclidean distance between quantities.

In a preferred embodiment, the above distance, or, error e_(i) may beobtained as∫f(Â _(z) −A _(z))² +f(Â _(y) −A _(y))² +f(Â _(x) −A _(x))² dti.e., a norm where to the quadratic distances between the components acost functional f is moreover applied to take into account specificaspects of the vehicle condition, understood as dynamic range, but alsoas type of manoeuvre and possibly other parameters such as conditions offriction or wind.

The above cost functional f may be implemented, for example, as aweighted measurement, i.e., as a weight applied to the norm or to themeasurement of distance, the weights being chosen on the basis ofobservations on standard manoeuvres carried out by the motor vehicle.

It should be pointed out that the evaluator 111 operates in the firstplace to calculate the closeness between the estimate and themeasurement supplied by each model. In this perspective, the costfunctional f represents a possible further degree of freedom that can beapplied to the evaluator 111 to render it more flexible in regard toparticular vehicle conditions. In theory, the model could be complex tothe point of taking into account every parameter of interest for theestimate and not require the above functional, or else a less flexibleestimate without the functional may be accepted. Hence, in variousembodiments, the aforesaid cost functional f is not present, or may beequal to 1 in the equation appearing above.

In various embodiments, the above cost functional f may be the same forall the models 11 ₁, . . . , 11 _(n).

In various embodiments, the aforesaid cost functional f is different fordifferent models associated to different dynamic ranges, to take intoaccount, for example, the specificity of certain manoeuvres associatedto those dynamic ranges and models. There may be applied to the blocks11 ₁, . . . , 11 _(n) functionals f_(j) that represent, for example, avehicle condition with low coefficient of friction, a condition ofhighspeed ring, or a condition of twist of the steering wheel.

In the example specifically described in FIG. 3, as has been said thevehicle model 11 ₁ may use a cost functional f that calculates an errore_(i) corresponding to∫f(Â _(yj) −A _(y))² +f(Â _(xj) −A _(x))² dtwhere Â_(yj,xj) is an estimate of the acceleration along the axes x andy for each model 11 _(j), A_(y,x) is the corresponding measurement madeby the inertial platform, and f is the cost functional.

The minimum min(e₁, e₂, . . . , e_(n)) of the error e_(j) evaluated inblock 111, determines the value assumed by the selection signal S, whichcorresponds to the choice of the model 11 _(i) associated to arespective dynamic range DR_(i) that best estimates the quantity at itsinput, and hence to the choice of the complementary filter 12 ₁, . . . ,12 _(n) to be used dynamically that best operates in the correspondingdynamic range DR_(i).

Each vehicle model 11 _(j) with j=1, . . . , n defines a particularvehicle condition whereby a given error e_(j) is the minimum for all themodels considered if the accelerations and angular velocities measuredderive from the vehicle condition associated to the corresponding model11 _(j). The vehicle model 11 _(j) identifies a particular dynamic rangeof the vehicle quantities A_(x), A_(y), A_(z), of the accelerationsignal A and of the angular velocities p, q, r measured. Furthermore,for each vehicle model 11 _(j) there exists just one filter 12 _(i) witha time constant τ defined for that particular vehicle condition.

In particular, for example, stored in the supervisor module 11 is alook-up table or other data structure that sets each of the vehiclemodels 11 ₁, . . . , 11 _(n) in relation with one of the filters 12 ₁, .. . , 12 _(n). It is envisaged to construct empirically the abovelook-up table by identifying, on the basis of the correctness of theestimator {circumflex over (x)}_(i) supplied at output, the value oftime constant τ that corresponds to a given dynamic range, i.e., thatenables a correct estimate of the angle of attitude, for example withina pre-defined error value. Hence, in the look-up table the vehicle model11 _(j) associated to that given dynamic range is set in relation withthe filter with time constant that enables correct estimation of theattitude in the context of the system 10. When the minimum min(e₁, e₂, .. . , e_(n)) of the error e_(j) indicates that a certain model 11 _(j)is the most suited to the dynamic range of the acceleration and/orgyroscopic signals at input, by accessing the look-up table with theindex of that model 11 _(j) at output there is obtained, as selectionsignal S, the index of the filter 12 _(i) with a time constant τ suitedto its dynamic range and hence to be selected to obtain the bestestimate of attitude.

The supervisor module 11 is obtained via a microprocessor module, forexample the ECU of the motor vehicle. Also the selector 14 may beintegrated within this microprocessor.

Illustrated in FIG. 2 is a detailed diagram of a complementary filter 12_(i). This complementary filter 12 _(i) comprises a module 121 forcomputing the angle of inclination, or tilt, which receives at input theacceleration signal A and supplies calculated values of the angles ofroll θ, pitch φ, and yaw ψ. This is achieved according to the followingrelations, in themselves known:

$\begin{matrix}{{\theta = {\arctan( \frac{A_{x}}{\sqrt{A_{y}^{2} + A_{z}^{2}}} )}}{\varphi = {\arctan( \frac{A_{y}}{\sqrt{A_{x}^{2} + A_{z}^{2}}} )}}{\psi = {\arctan( \frac{\sqrt{A_{x}^{2} + A_{y}^{2}}}{A_{z}} )}}} & (1)\end{matrix}$

The complementary filter 12 _(i) further comprises a module forcomputing attitude rates 126, which receives at input theangular-velocity signal ω and performs the calculation of the values ofthe first derivatives of the angles of roll θ, pitch φ, and yaw ψ, i.e.,{dot over (θ)}, {dot over (φ)}, {dot over (ψ)}. The attitude-ratecomputing module 126 makes, in particular, the following calculation:

$\begin{matrix}\overset{.}{\phi = {p + {\tan\;{\theta( {{q\mspace{11mu}\sin\;\psi} + {r\;\cos\;\psi}} )}}}} & (2) \\{\overset{.}{\theta} = {{q\;\cos\;\varphi} - {r\;\sin\;\varphi}}} & \; \\{\overset{.}{\psi} = \frac{{q\;\sin\;\varphi} + {r\;\cos\;\varphi}}{\cos\;\theta}} & \;\end{matrix}$

From the angular velocities p, q, r measured by the gyroscope and fromthe values of the angles of attitude, or Euler angles, it is possible tomeasure the attitude rates, i.e., the first derivatives {dot over (θ)},{dot over (φ)}, {dot over (ψ)} of the Euler angles using Eqs. (2), whichare in themselves known.

In particular, the above Eqs. (2) may be written in matrix form as:

$\begin{matrix}{{\begin{matrix}\overset{.}{\varphi} \\\overset{.}{\theta} \\\overset{.}{\psi}\end{matrix}} = {{A^{- 1}( {\varphi,\theta,\psi} )}{\begin{matrix}p \\q \\r\end{matrix}}}} & (3)\end{matrix}$taking into account that

$\begin{matrix}{{A^{- 1}( {\varphi,\theta,\psi} )} = {\begin{matrix}{\cos\;(\theta)} & 0 & {\sin\;(\theta)} \\{\sin\;(\theta)\tan\;(\varphi)} & 1 & {{- \cos}\;(\theta){\tan(\varphi)}} \\{- \frac{\sin(\theta)}{\cos\;(\varphi)}} & 0 & \frac{\cos\;(\theta)}{\cos\;(\varphi)}\end{matrix}}} & (4)\end{matrix}$

The relations (3) and (4) represent the construction of block 126, thematrix A⁻¹ being the matrix of rotation that enables calculation of theangular velocities {dot over (θ)}, {dot over (φ)}, {dot over (ψ)} in thevehicle reference system starting from the angular velocities p, q, rmeasured by the gyroscope (sensor reference system) and from theestimate of the angles of roll θ and pitch φ.

The calculated values of the angles of roll θ, pitch φ, and yaw ψ aresupplied by the tilt-angle computing module 121 at input, as set-point,to a control loop that as a whole constitutes a complementary lowpassfilter and a complementary highpass filter, through a derivator block123, with time constant τ, and an integrator block 125. Specifically,the aforesaid calculated values of the angles of roll θ, pitch φ, andyaw ψ are supplied at input, as set-point, to an adder node 122, whichcomputes the difference with respect to the estimate x _(i) at outputfrom the complementary filter 12 _(i). The corresponding differencesignal D is supplied at input to the derivator 123, which has a timeconstant τ. The output of the derivator 123 is supplied to a secondadder node 122, which adds it to the attitude rates {dot over (θ)}, {dotover (φ)}, {dot over (ψ)} supplied at output from the attitude-ratecomputing module 126. The corresponding addition signal M is supplied tothe integrator 125, which supplies at output the estimate of the angleof attitude of the vehicle {circumflex over (x)}_(i).

Hence, the complementary filter 12 _(i) is in this way used forcombining two independent measurements that are in themselves noisy,i.e., the acceleration signal A supplied by the accelerometer and theangular-velocity signal ω supplied by the gyroscope, where eachmeasurement is corrupted by different types of spectral noise. Thefilter 12 _(i) provides an estimate of the real angle of attitude of thevehicle {circumflex over (x)}_(i) via the two complementary highpass andlowpass filters with time constant τ.

The values of the angles of roll θ, pitch φ, and yaw ψ are suppliedalready directly by the tilt-angle computing module 121 on the basis ofthe acceleration signal A. This measurement, however, is accurate onlyat low dynamics.

The time constant τ according to a main aspect of the solution describedherein is set different for each filter 12 _(i) so as to tune therespective filter to a different dynamic range of the input signals Aand co.

Hence, from what has been described above, the advantages of thesolution proposed emerge clearly.

The device for detecting the attitude of motor vehicles via the use of abank of complementary filters enables use of filters with a lower degreeof complexity, maintaining the performance of extended Kalman filters.

The device for detecting the attitude of motor vehicles, as compared tothe extended Kalman filter used in applications linked to the dynamicsof the motor vehicle, guarantees levels of performance that fully meetthe specifications, but with a reduction of the complexity of tuning ofthe filters and of the use of computational resources.

The device for detecting the attitude of motor vehicles based upon anapproach of the ‘Data Fusion’ type combines the measurements ofgyroscopic and acceleration sensors present on board the vehicle in theframework of an inertial navigation system (INS), increasing andadvantageously enriching each of the above measurements, so that thereis obtained, for the vehicle, a powerful system of positioning of theattitude on three axes.

The estimate of attitude can be used for continuous mobile positioningobtained with the IMU.

The stable relative position supplied by the INS can then be used asbridge information for covering periods of time during which a navigatorbased upon GNSS signals, in particular GPS signals, receives degradedsignals or these signals are not available.

The invention has been described in an illustrative manner. It is to beunderstood that the terminology which has been used is intended to be inthe nature of words of description rather than of limitation. Manymodifications and variations of the invention are possible in light ofthe above teachings. Therefore, within the scope of the appended claims,the invention may be practiced other than as specifically described.

The invention claimed is:
 1. A device for detecting the attitude ofmotor vehicles that comprises: using at least one filter of acomplementary type for computing an estimate ({circumflex over (x)}_(i))of angles of attitude (θ, φ, ψ) of the motor vehicle as a function ofinput signals including an acceleration signal (A) and anangular-velocity signal (ω); said device including a plurality ofcomplementary filters, each tuned for operating in a specific dynamicrange; and a supervisor module, adapted to recognise the dynamic rangeof the input signals (A, ω) and select a corresponding filter in saidplurality of complementary filters, receiving the acceleration signal(A) and the angular-velocity signal (ω) measured by respective sensorsand, on the basis of the values of said input signals (A, ω), controls aselector so that it selects one of the estimates ({circumflex over(x)}_(i)) available at the outputs of said plurality of complementaryfilters as output (U) of the attitude-detection device; said supervisormodule including a plurality of models of the vehicle defined as afunction of dynamic quantities of the vehicle that affect the value ofthe attitude, each of said models generating an estimate of the dynamicquantities (Â_(x), Â_(y), Â_(z)) comprising one or more of theacceleration values (Ax, Ay, Az) and/or of the gyroscope signals (p, q,r), said supervisor module further including a module for evaluating themodel in said plurality of models that best estimates the currentcondition (DR_(i)) of the vehicle, and selecting a corresponding filterfrom said plurality of complementary filters on the basis of saidevaluation.
 2. The device as set forth in claim 1, wherein saidsupervisor module that acts to detect the level (Ax, Ay, Az) of theacceleration signal (A) and the level (p, q, r) of the angular velocity(ω) and select, on the basis of said levels, the complementary filter tobe used in the estimate of attitude from said plurality of complementaryfilters.
 3. The device as set forth in claim 2, wherein saidcomplementary filter comprises a module for computing the angle ofinclination, or tilt, which receives at input the acceleration signal(A) and is adapted for supplying calculated values of the angles of roll(θ), pitch (φ), and yaw (ψ), and a module for computing attitude rates,which receives at input the angular-velocity signal (ω) and is adaptedfor computing the values of the first derivatives ({dot over (θ)}, {dotover (φ)}, {dot over (ψ)}) of said angles of roll (θ), pitch (φ), andyaw (ψ), said tilt-angle computing module and said attitude-ratecomputing module supplying said outputs to a control loop comprisingcomplementary filters.
 4. The device as set forth in claim 3, whereinthe output of said tilt-angle computing module is supplied as set-pointto the control loop for generating a difference signal (D) with respectto the estimate of attitude at output from the control loop, while thesignal at output from the attitude-rate computing module is added to theoutput of a derivator block, which receives at input said differencesignal (D), a resulting addition signal being supplied as input to anintegrator, which generates said estimate of the angle of attitude ofthe vehicle ({circumflex over (x)}_(i)).
 5. The device as set forth inclaim 3, wherein said control loop acts as a complementary lowpassfilter and a complementary highpass filter, the time constant (τ) ofwhich is set for tuning the filter with respect to a given dynamicrange.
 6. The device as set forth in claim 1, wherein said supervisormodule comprises a plurality of different models of the vehicle thatestimate one or more of the acceleration values (Ax, Ay, Az) and/or ofthe gyroscope signals (p, q, r) on the basis of measured values ofdynamic quantities of the vehicle that affect the value of the attitude.7. The device as set forth in claim 6, wherein said evaluation module isadapted for measuring an error (e₁, . . . , e_(n)) of each modelcalculated as distance of estimates (Â_(x), Â_(y), Â_(z)) of each modelfrom the values (Ax, Ay, Az) effectively measured and for identifyingthe minimum value (min (e₁, e₂, . . . , e_(n))) of said error (e₁, . . ., e_(n)) and the corresponding model.
 8. The device as set forth inclaim 7, wherein said evaluation module is adapted for applying in thecalculation of said distances (e₁, . . . , e_(n)) a cost functional (f)associated to a given condition of the vehicle, in particular a weightedmeasurement, the weights of which are chosen on the basis ofobservations on manoeuvres made by the motor vehicle.
 9. The device asset forth in claim 1, wherein it is comprised in an inertial navigationsystem of a motor vehicle.